It's genuinely hard to do split screen on lower spec hardware and still hit your target framerate / avoid running out of memory for many games. The article mentions this briefly, but it's been a problem for high profile titles very recently (Baldur's Gate 3 for one)
It's mostly a matter of priorities and trade-offs. Super Nintendo and Nintendo 64 could handle split screen on hardware that was much crappier than anything you would be able to buy today.
Of course, they did that by dialing down the graphics.
If split screen is not the main focus of the game, the engineering effort to even make these trade-offs would be mostly wasted.
That's the real answer, it's compromise and priorities. Modern hardware could do 16, 32 player Mario Kart 64 on a single machine easily, but the manufacturers set a minimum for visual fidelity that the hardware cannot handle.
Recent examples are some of the Switch console sellers (Zelda and Pokemon), both of which have framerate issues. Not because the games are that pretty (personal opinion), but because their developers did not prioritize performance.
Yes. Though keep in mind that developers only have finite resources (and that includes latency, ie calendar time until they need to ship). So if you prioritize performance, something else gets less attention.
It's up to you as a player / customer to decide whether you like the trade-off offered.
